In 1917 the armies on the Western Front continued to change their fighting methods due to the consequences of increases in fire-power, greater numbers of automatic weapons, the decentralisation of authority and the integration of specialised branches, equipment and techniques into the traditional structures of infantry, artillery and cavalry. Tanks, railways, aircraft, lorries, chemicals, concrete and steel, photography, wireless and advances in medical science increased in importance in all of the armies, as did the influence of the material constraints of geography, climate, demography and economics. All of the armies encountered growing manpower shortages, caused by the need to replace the losses of 1916 and by the competing demands for labour of civilian industry and agriculture. The c